This invention relates to a ventilation control apparatus for an animal enclosure, such as a poultry house. The application also describes a method by which ventilation is controlled within any such an animal enclosure.
Proper ventilation in a poultry enclosure results in higher production, better quality, improved feed conversion, less disease and lower mortality rates. Poultry are particularly sensitive to changes in ventilation conditions for a number of reasons. First, all birds have a very high metabolism rate. This results in the rapid build-up of respiration waste products, particularly carbon dioxide. Since carbon dioxide is heavier than the ambient air, the carbon dioxide tends to accumulate from the enclosure surface upwardly. Since poultry have short legs and are therefore close to the floor, the carbon dioxide layer can very rapidly accumulate to a point where the poultry are submerged in a blanket of carbon dioxide. Because of the high respiration and metabolism rates of the poultry, the poultry very quickly suffocate. Even in less extreme cases, too little ventilation creates gas fumes and ammonia which will weaken the birds and increase mortality from secondary causes.
Of course, build-up of carbon dioxide, moisture and gas fumes can be eliminated by constant ventilation. However, too much ventilation drastically decreases productivity by wasting heat and decreasing feed conversion rates. As is apparent, to the extent the poultry must use calories to maintain their body heat, those calories are not available for adding weight. Between the two extremes of no ventilation and too much ventilation, there exists an ideal ventilation rate at which the air exchange is sufficient to remove gases, provide replacement oxygen and remove moisture while maintaining the feed conversion rate by minimizing the number of calories which must be expended by the poultry for maintenance of body temperature.
A properly regulated ventilation system should have the capacity to produce the proper ventilation at any given temperature; automatically adjust the ventilation rate in response to changing outdoor conditions, control moisture, gas and ammonia buildup; properly mix and distribute fresh outside air to maintain a uniform and healthy environment throughout the entire enclosure and reduce the supervision and labor necessary to regulate the proper ventilation rate and temperature. The goal of regulating the ventilation system is to arrive at a minimum ventilation rate and to maintain that rate as the temperature varies during any given day and also as the temperature varies from day to day and week to week during the growth cycle of the poultry. Aside from providing replacement oxygen and removing fumes and toxic gases, removal of moisture is a critical factor in maintaining proper ventilation. The temperature of air greatly affects its ability to hold water. As a general rule, for every 20.degree. F. (11.degree. C.) rise in the dry bulb temperature of air, its ability to hold moisture doubles. Continued reduction in airflow rate will increase the water removal rate until the losses of heat through the ceiling and walls of the animal enclosure prevents further proportionate increases in temperature in the house. At this point, the water removal rate begins to be reduced. Of course, with no airflow, no water can be removed. Therefore, especially in winter, the optimum flow rate for maximum moisture removal varies from day to day depending upon outdoor climatic conditions and construction of the animal enclosure. Either too much or too little airflow results in excess moisture. In the summer, the air temperature is usually high enough to have good moisture holding capacity and all that is required is that the air within the animal enclosure be exchanged at an adequate rate to provide for sufficient replacement oxygen and gas removal.
it is also important to maintain a suitable temperature within the animal enclosure which is above the outdoor temperature in winter and is low as is economically feasible in summer. In winter, the ventilation system uses part of the birds' own body heat to warm the incoming air and evaporate and remove moisture. In summer, the ventilation system must remove all of the heat generated by the poultry plus the solar heat which is transmitted into the enclosure through the walls and roof. Therefore, a much larger airflow rate is needed during summer to keep the building temperature within the range of the outdoor temperature. Establishing proper ventilation is accomplished by computing the cubic feet per minute of total airflow necessary to provide the minimum ventilation efficiency discussed above. Using prior art methods and equipment, tables are used which provide information concerning the ventilation required at various ages and outside temperatures to eliminate moisture produced by poultry and to provide sufficient fresh uncontaminated replacement air. The proper ventilation rate is then expressed as a percentage of the total cubic feet per minute of airflow a ventilation system will produce if operating 100% of the time. By determining this figure a timer (usually a ten minute timer) is set so that, for example, if a system has a total airflow capacity of 10,000 cfm (300 cubic meters per minute) and 3,000 cfm (90 cmm) of airflow is computed to be sufficient, the ten minute timer is set to operate the ventilation fans for three minutes during each consecutive ten minute timing cycle. The problem with this approach is that these figures are based on a given outside temperature, for example 70.degree. F. (22.degree. C.). The control unit is then left unattended for a period of one week. Based upon the setting, the ventilation fans operate the same amount of time during each ten minute cycle day and night throughout the entire week. Then, the setting is adjusted to take into account the fact that the birds are one week older, have different oxygen demands and produce larger quantities of carbon dioxide and droppings.
However, this type of setting provides only a crude approximation of ideal conditions. During any given day the outside air temperature can vary 20.degree. F. to 30.degree. F. (11.degree. C. to 16.degree. C.). As mentioned above, the air retaining capacity of air doubles for every 20.degree. F. (11.degree. C.) rise in temperature and, conversely, is reduced by half for each 20.degree. F. (11.degree. C.) drop in temperature. Therefore, the system will be operating at the desired efficiency only for a relatively short period of time during each day even if overall weather conditions remain unchanged simply because of the variation in daytime and nighttime temperatures.
In accordance with the invention described below, an outside air temperature sensor constantly transmits temperature information to an adjustment means. As a result, the percentage of operation time is constantly varied so that the ventilation fans or other output devices vary in operation time to take into account even very slight changes in outside air temperature. This results in a much more efficient ventilation system which minimizes power requirements and optimizes feed conversion rates and poultry mortality.